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Petrifilm Counts with the Apogee BioCount System: Minimum Incubation Time

BioCount is a software program that uses image analysis technology to accurately and precisely determine the number of microbial colonies on Petrifilm media. This study establishes culture and dilution parameters for reproducible colony counts and determines the minimum incubation time needed to detect colonies on Petrifilm. Results show that automated counting with BioCount is as effective as manual counting but does not decrease the minimum incubation time required for colony formation.

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Petrifilm Counts with the Apogee BioCount System: Minimum Incubation Time

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  1. Petrifilm Counts with the Apogee BioCount System:Minimum Incubation Time Joy Elbert and J. D. Hendrix Kennesaw State University

  2. BioCount: A software program that uses image analysis technology to determine the number of microbial colonies in a petri dish. Determines the number of colonies with accuracy and precision comparable to a manual count. Background

  3. Previous Study • Saadat and Hendrix determined that the BioCount system accurately counted total aerobic colonies on Petrifilm media • Parameters were optimized to allow the program to detect an accurate number of colonies on the Petrifilm media

  4. Petrifilm • Developed By 3M • Rehydratable sample-ready media • Used for environmental and industrial purposes • 24 hour incubation required to count colonies accurately • Selective and/or differential medium

  5. Current Methods • Require a diluted sample of the microorganism spread evenly over the surface of a medium • Cells or groups of cells form colonies (“Colony Forming Units”) • The initial number of microorganisms can be calculated

  6. Objectives • Establish culture and dilution parameters to give a reproducible count of 20 - 200 colonies per film • Determine the minimum incubation time needed to detect colonies on Petrifilm • Compare manual and automated counts of colonies at different incubation times

  7. Procedure • Turbid broth cultures of Escherichia coli (24 hr, 37°C in tryptic soy broth) were diluted 10-5, 10-6, 10-7, 10-8, and 10-9 • 0.5 ml samples were plated on 3M Petrifilm (“Total Aerobic” films) and incubated at 37°C for time intervals between 6 and 24 hr • Colony counts were determined by manual and automated methods

  8. Results • Optimal dilution was determined on films incubated for 24 hr • At 10-7 dilution the colonies remained in the range of 50 to 80 (0.5 ml volume plated)

  9. Results

  10. Results

  11. Results

  12. Results

  13. Results • The t-test was used to determine if there was a significant difference between the manual and automated counts • For 29 films counted:t = 0.38 • There was no significant difference between manual and automated counts

  14. Conclusions • To detect Escherichia coli colonies on total aerobic Petrifilm, a minimum incubation time of 12 hr is required • There was no significant difference between manual and automated counts • Using automated counting is more rapid than manual counting, but it does not decrease the minimum incubation time needed to form the bacterial colonies

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